Proton spin-lattice and spin-spin relaxation times(T1 and T2, respectively) of cells and tissues are mainly affected by free or bulk water molecules in the intra-and extra-cellular environment and hydration water molecules which interact with macromolecules. It is assumed that, to a first approximation, the reciprocal of T1 (or T2) of cells or tissues is the linear sum of the reciprocals of T1 (or T2) of these water components. Thus, we hypothesize that change in the ratio of the amount of hydration water to that of bulk water or structural change in conformation of macromolecules in a biological system may lead to an alternation of its apparent proton relaxation times. These biological changes may occur in cells and tumor due to physiological constraints or to damage caused by radiation and chemotherapeutic drugs. In this proposed study, we examine the proton relaxation times of mammalian cells which are present in a variety of physiological conditions (e.g. different phases in the division cycle, logarithmic- and plateau-phase growth. amd quiescent and proliferative states). We also measure T1 and T2 of mouse solid tumors and their neoplastic and host subpopulations. Following these background studies, we will investigate the correlations of T1 and T2 with radiation- and adriamycin-induced cell-age redistribution, G2 accumulation, and necrotic processes in the same biological systems. In addition, the change of T1 and T2 relative to transition of quiescent population to proliferative one will be examined. Finally, the radiation effects in tumors will be further studied by in vivo NMR imaging and subsequent analysis of the T1 and T2 so derived. The goal of these systematic studies is to establish the potential utilization of proton NMR relaxation techniques in probing radiation damage, and the extent to which NMR imaging is sensitive to the related applications.